This invention relates to an automatic tensioner for applying a tension to a belt such as a drive belt of an engine for a vehicle.
A conventional automatic tensioner is disclosed, for example, as illustrated in FIG. 1 (refer to Japanese Patent Publication No. SHO 02-2182). In FIG. 1, an automatic tensioner 1 is arranged as follows. That is, an arm 3 has a proximal section 3a which is mounted on a cylindrical housing 2 for angular movement thereabout. The arm 3 has a free end thereof adjacent to which an idler pulley 4 is mounted for angular movement. A torsion coil spring S is arranged between the housing 2 and the proximal section 3a of the arm 3, for applying a tension to a belt through the idler pulley 4. In order to angularly move smoothly the arm 3 with respect to the housing 2, a resin sleeve 6 is fitted into an annular space defined between an outer peripheral surface of the housing 2 and an inner peripheral surface of the proximal section 3a of the arm 3, which faces toward the outer peripheral surface of the housing 2.
The conventional automatic tensioner described above has the following problems. That is, since the arm 3 is moved angularly about the resin sleeve 6 which serves as a center of angular movement, as the resin sleeve 6 is worn off in a one-sided manner, mounting rattle occurs in the arm 3. Thus, nonuniformity in angular movement occurs in the arm 3, so that there is a fear that the tension on the belt is fluctuated.
For the reason discussed above, the resin sleeve 6 is required which is not only large in diameter, but also large in an axial direction, in an attempt to reduce a surface pressure of the resin sleeve C. Accordingly the automatic tensioner 1 becomes large in construction.